With the rapid advance of wireless communication technology and the evolution of communication system, LTE is attracting a lot of interest as one of the most promising 4th Generation mobile communication technologies. In order to meet the increasing traffic demand, the LTE system adopts various technologies including carrier aggregation. Carrier aggregation is enabling to one or more secondary carriers along with one primary carrier, unlike the conventional system using one carrier for communication between a User Equipment (UE) and an evolved Node B (eNB), to increase the data rate in proportion to the number of secondary carriers. In LTE, the primary carrier is referred to as Primary Cell (PCell) and the secondary carrier as Secondary Cell (SCell).
Meanwhile, in the case of transmitting data in PCell and SCell simultaneously, this brings some problems such as how to perform Random Access (RA) and Sounding Reference Signal (SRS) transmission and how to determine transmission power.
Particularly in the case of the Carrier Aggregation (CA) between PCell operating in Time Division Duplex (TDD) and TDD SCell or between TDD SCells, it may occur that downlink and uplink reception and transmission have to be performed simultaneously depending on the TDD configuration, and this functionality may not be supported depending on the UE capability.
Furthermore, in the case that there is any change in the positions of the eNB devices managing the PCell and SCell due to the deployment of repeaters and Remote Radio Heads (RRHs), the uplink transmission timing may vary and thus it is necessary to measure downlink reference signal and report the measurement result. There is therefore a need of specifying detailed operations to solve the above problems.